Nowadays, technological advances have enabled people to get connected to the Internet anytime and anywhere. In fact, people are relying more and more on the continued connectivity to the Internet in different faces of our everyday lives: for business, for study, for entertainment, and for personal use. To such ends, recent development in wireless technologies even allows us to get connected while on the move. Multimode terminals with the ability to connect to the Internet using a wide range of access technologies, such as Third Generation (3G) cellular networks, General Packet Radio Service (CPRS), IEEE 802.11a/b/g and Bluetooth are also getting more popular.
Various portable computing devices such as handheld mobiles, laptops and personal digital assistants (PDAs) with enhanced networking capabilities have increased the demand for seamless communication both in wired and wireless networks. Increased use of multimedia contents such as video conferencing makes seamless communication an essential and required feature in mobile connections. Practical mobility management should provide seamless handoff where the user does not observe communication disruptions. Today's mobile data networks commonly consist of several wireless overlapping networks, supporting different data rates and geographical coverage and can only be accessed via media specific air interfaces.
Many devices today communicate with each other using the Internet Protocol (IP). In order to provide mobility support to mobile devices, the Internet Engineering Task Force (IETF) has developed the Mobility Support in IPv6 (see the following Non-patent Document 1). In Mobile IP, each mobile node has a permanent home domain. When the mobile node is attached to its home network, it is assigned a primary global address known as a home address (HoA). In this specification, the situation that the mobile node is attached to its home network is also called “at home”.
When the mobile node is away, i.e. attached to some other foreign networks, it is usually assigned a temporary global address known as a care-of address (CoA). The idea of mobility support is such that the mobile node can be reached at the HoA even when it is attached to other foreign networks.
This is done in the Non-patent Document 1 with an introduction of an entity at the home network known as a home agent (HA). Mobile node registers its CoA with the home agent using messages known as Binding Updates (BU). This allows the home agent to create a binding between the HoA and CoA of the mobile node. The home agent is responsible to intercept messages that are addressed to the mobile node's HoA, and forward the packet to the mobile node's CoA using packet encapsulation (i.e. putting one packet as the payload of a new packet, also known as packet tunneling).
Binding Update messages can also be sent to the peer the mobile node is communicating with, known as the correspondent node (CN), so the correspondent node can send packets meant for the home address of the mobile node to the care-of address of the mobile node.    [Patent Document 1] European Patent Publication EP1432198    [Patent Document 2] PCT Patent Publication WO 00/42755    [Patent Document 3] Publication of US Patent Application 2004-0142657    [Non-patent Document 1] Johnson, D. B., Perkins, C. E., and Arkko, J., “Mobility Support in IPv6”, Internet Engineering Task Force Request For Comments 3775, June 2004.    [Non-patent Document 2] Wakikawa, R., “Multiple Care-of Addresses Registration”, Internet Draft: draft-wakikawa-mobileip-multiplecoa-03.txt (expired), July 2004.
Mobile IPv6, however, is ill-suited to take advantage of the fact that a mobile node can have multiple access interfaces, which is getting more and more common. For instance, all notebook computers these days have both 802.11/ab/g and Bluetooth interfaces. Phones with 3G, bluetooth, and wireless-LAN capabilities are already beginning to appear in the market.
A few prior arts have attempted to make use of multiple access interfaces with Mobile IP. The Patent Document 1 describes a method of handover of flows using different home addresses. Although this allows the mobile node to make use of multiple accesses to ease handovers, it does not describe how a mobile node can use both interfaces simultaneously.
For that, the Patent Document 2 proposes a mechanism that allows the mobile node to transmit connectivity information to its home agent, thus allowing its home agent to forward packets according to such connectivity information. This is, however, restricted to only the home agent. It is unclear how the correspondent node can receive such connectivity information.
The Patent Document 3 describes a method for the mobile node to selectively register different care-of addresses with its home agent and correspondent node. The Non-Patent Document 2 suggests a way for a mobile node to bind multiple care-of addresses to the same home address at the home agent and correspondent node.
Although the Patent Document 3 and Non-Patent document 2 specify ways for a mobile node to make use of multiple addresses at once, they suffer from two main constraints.
Firstly, care-of address registration cannot be used when one of the interfaces is at home. It is a common scenario for a mobile device to have a wireless-LAN interface for hotspot surfing, and a 3G (or GPRS) connection. It is usually the 3G connection that provides Mobile IP services. However, as 3G and GPRS services typically have a wide coverage, the mobile device is usually connected to its home network most of the time. In such cases, both the Patent Document 3 and Non-Patent document 2 cannot be used.
Secondly, both the Patent Document 3 and Non-Patent document 2 rely on the existence of home agents. Although it is a growing trend among service providers to provide Mobile IP services, many cellular operators have yet to offer home agent services to their subscribers. When there is no home agent available, both the Patent Document 3 and Non-Patent document 2 cannot be used.